- Range (particle radiation)
In passing through matter,
charged particles ionize and thus lose energyin many steps, until their energy is (almost) zero. The distance to this point is called the range of the particle. The range depends on the type of particle, on its initial energy and on the material which it passes.
For example, if the ionising particle passing through the material is a positive
ionlike alpha particleor proton, it will collide with atomic electrons in the material via Coulombic interaction. Since the mass of the protonor alpha particleis much greater than that of the electron, there will be no significant deviation from the radiation's incident path and very little kinetic energywill be lost in each collision. As such, it will take many successive collisions for such heavy ionising radiation to come to a halt within the stopping medium or material. Maximum energy loss will take place in a head on collision with an electron.
Since large angle scattering is rare for positive ions, a range may be well defined for that
radiation, depending on its energyand charge, as well as the ionisation energyof the stopping medium. Since the nature of such interactions is statistical, the number of collisions required to bring a radiation particle to rest within the medium will vary slightly with each particle, i.e. some may travel further and undergo less collisions than others. Hence, there will be a small variation in the range, known as straggling.
The energy loss per unit distance (and hence, the density of ionization), or stopping power also depends on the type and energy of the particle and on the material. Usually, the energy loss per unit distance increases while the particle slows down. The curve describing this fact is called the Bragg curve. Shortly before the end, the energy loss passes through a maximum, the
Bragg Peak, and then drops to zero (see the figures in Bragg Peakand in stopping power). This fact is of great practical importance for radiation therapy.
The range of
alpha particlesin ambient air amounts to several centimeters, this type of radiation can therefore be stopped already by a sheet of paper. Although beta particles scatter much more than alpha particles, a range can still be defined; it, frequently amounts to several hundred centimeters of air.
The mean range can be calculated by integrating the inverse stopping power over energy.
Wikimedia Foundation. 2010.
Look at other dictionaries:
Particle radiation — is the radiation of energy by means of fast moving subatomic particles. Particle radiation is referred to as a particle beam if the particles are all moving in the same direction, similar to a light beam.Due to the wave particle duality, all… … Wikipedia
Stopping power (particle radiation) — In passing through matter, fast charged particles ionize the atoms or molecules which they encounter. Thus, the fast particles gradually lose energy in many small steps. Stopping power is defined as the average energy loss of the particle per… … Wikipedia
range — /raynj/, n., adj., v., ranged, ranging. n. 1. the extent to which or the limits between which variation is possible: the range of steel prices; a wide range of styles. 2. the extent or scope of the operation or action of something: within range… … Universalium
Radiation length — In physics, the radiation length is a characteristic of a material, related to the energy loss of high energy, electromagnetic interacting particles with it.DefinitionHigh energy electrons predominantly lose energy in matterby bremsstrahlung, and … Wikipedia
Range — Contents 1 Mathematics, science, and technology 1.1 In mathematics 1 … Wikipedia
Radiation therapy — Radiation (medicine) redirects here. It is not to be confused with Radiation (pain) or Radiology. Radiation therapy Intervention ICD 10 PCS D ICD 9 CM … Wikipedia
Radiation hardening — is a method of designing and testing electronic components and systems to make them resistant to damage or malfunctions caused by ionizing radiation (particle radiation and high energy electromagnetic radiation), such as would be encountered… … Wikipedia
radiation measurement — ▪ technology Introduction technique for detecting the intensity and characteristics of ionizing radiation, such as alpha, beta, and gamma rays or neutrons, for the purpose of measurement. The term ionizing radiation refers to those… … Universalium
Particle therapy — Intervention ICD 9: 92.26 Particle therapy is a form of external beam radiotherapy using beams of energetic protons, neutrons, or positive ions for cancer treatment. The most common … Wikipedia
Radiation burn — Classification and external resources ICD 9 990 … Wikipedia